The overall objective of the proposed experiments is to characterize ultrasonic communication in mice. The mouse is widely used in studies of the auditory system and is thought to be a good model for human communication and audition, yet we know very little about the nature of the mouse's acoustic world. Humans characterizing the vocalizations of mice have been known to place the calls into anywhere from three to six total categories of vocalization types. The proposed studies will avoid human-based categorizations by asking the mouse directly whether they can discriminate or identify calls and whether they have enhanced capabilities for perceptually processing call-like sounds. Ultrasonic vocalizations from juveniles and adults will be recorded and then those same vocalizations will be used in perceptual studies in awake, behaving mice. These studies are urgently needed in the field of audition because so many laboratories regularly use the mouse as a model for hearing and communication in humans and now the differences and commonalities between the two species can be understood and utilized.